1. Field of the Invention
A tube extractor is disclosed of the hydraulically actuated type which removes tubes from a tube sheet of a heat exchanger by the expansion of a broach into the wall of the tube and then withdrawing the tube from the tube sheet.
2. Description of the Prior Art
A typical heat exchanger can utilize an outer shell with tube sheets at each end and tubes running from one end to the other which have their ends secured in the tube sheets by mechanical expansion or swaging. Heating or cooling mediums can pass over the tubes with fluid passing through the tubes to be cooled or heated. It is important that the heating or cooling medium and fluid not mix so that a close fit of the tube ends in the tube sheets is therefore quite important. The tubes are usually closely spaced together and in a typical example for three quarters inch diameter tubes on one inch centers in a three foot diameter tube sheet, some one thousand holes would be present in the tube sheet. Due to the corrosive and abrasive nature of the materials involved the tubes must be periodically replaced.
To replace the tubes they are generally cut between the tube ends and the expanded ends of the tubes forcibly withdrawn from the tube sheets an inch or two until they can be withdrawn by hand.
Various tools have been suggested for removing these tubes, a typical tool being shown in the U.S. Pat. to Armstrong, No. 2,697,872, which uses grippers having an internal taper at the forward end, arranged circumferentially around a rod and having a forwardly divergent conical surface, as is shown in FIGS. 2 and 4. Gripper claws 22 are held stationary as tension is applied to the rod 30, which action wedges the grippers into crushing contact with the inside diameter of the tube. A second piston then applies tension to the grippers directly to pull out the tube.
The Armstrong structure is subject to various problems as the mandrel is necessarily larger in diameter under the teeth, since it is forwardly divergent, which means that there is less cross section available for the grippers, which makes them more prone to breakage. In addition, tensile loading of the Armstrong mandrel makes it inherently fragile, since for the same cross section, most materials are stronger in compression than in tension. In the event of bad adjustment leading to failure of the mandrel, it will neck down and part with a snap. The forward part of it would then shoot out the front of the gun, with high velocity, and pose a very real hazard to a person working at the other end of the tube.
The U.S. Pat. to Miller, No. 3,613,212, illustrates the use of a tap of unusual shape for removing tubes from tube sheets wherein a threaded rotatable tap is engaged with the tube by turning and the tap and its mounting are then withdrawn. The Miller structure however does not illustrate any means of removing the tap and tube other than manual which would require considerable force to withdraw the tube from the tube sheet, is slow and could involve problems of getting the tube end off of the tap after withdrawal.
The U.S. Pat. to Chuplis, Jr., No. 3,120,700, illustrates a tube puller with a rotatable tap similar to Miller but does not use a tap of unusual shape as is disclosed in Miller.
The U.S. Pat. to Sipher, No. 3,367,011, illustrates a tube pulling device similar to Armstrong which utilizes gripper jaws which are expanded outwardly into the tube wall with the jaws longitudinally stationary producing a crushing action with high radial forces.
The U.S. Pat. to Keys, No. 3,791,011, shows a tube pulling device similar to and with the same limitations as Armstrong with longitudinally fixed radial expansion of gripping means into the tube wall and withdrawal of the tube end from the tube sheet.
The U.S. Pat. to Stellatella, No. 3,507,028, shows a hydraulic tube puller with radial expansion of an inner end portion of a tube gripping member into the tube wall similar to and with the same limitations as Armstrong.
The U.S. Pat. to Sismore, No. 3,835,520, shows the use of gripper jaws similar to Armstrong's, wedged into crushing contact by a forwardly divergent bar or mandrel.
The primary problem with all the structures shown in the prior art is that they impose an expansion force on the tube precisely at the point where it is engaged with the tube sheet which can adversely affect the thin ligament of metal between adjacent holes and cause the holes in the tube sheet to enlarge and not properly grip a new tube when it is expanded.
The apparatus of my invention, if properly adjusted, does not expand the tube ends radially but securely grips the tubes by the combined radial and axial movement of the cutting teeth for withdrawal, and possesses many other advantages.